In manufacturing a semiconductor element, it has been considered the possibilities of using a droplet discharge device for forming a pattern of a thin film or a wiring, each of which is used for a semiconductor element, to reduce costs for equipment and to simplify a manufacturing process.
In this instance, various wirings such as a gate electrode, a scanning line, a signal line, and a pixel electrode for forming a semiconductor element are formed according to the procedure, that is, a composite formed by dissolving or dispersing a conductive material into a solvent is discharged from a nozzle of a droplet discharge device to the above of a substrate or a film so as to directly draw such various wirings (See, for example, Japanese Patent Application Laid-open No. 2003-126760).
To manufacture a semiconductor element such as a thin film transistor (TFT) that is used for a display device as typified by an active matrix liquid crystal display (LCD) device or an active matrix electroluminescent display device, it has been required to establish a structure and a process that are most appropriate to droplet discharging and that are different from a TFT manufactured by conducting repeatedly a film formation process, a patterning process, and an etching process. It has been required to simplify the structure and the process of a TFT manufactured by a droplet discharging with the increase in the size of a TFT substrate, for example, a substrate of more than 1×1 m or twice or three times as large as that.
Especially, in case that the foregoing TFT is formed to have an inversely staggered type (bottom gate type) as typified by a channel protecting type or a channel etching type, a semiconductor film and a semiconductor film containing n-type impurities are formed all over a substrate; and the formed semiconductor films are etched using a resist mask to form an island-like semiconductor region; then, the formed semiconductor film containing n-type impurities is divided into a source region and a drain region using a metal mask or the like. Hence, a resist mask is required to be formed by an exposing, developing, and droplet discharging in forming an island-like semiconductor region. It results in the increase in the number of processes and the number of kinds of materials.
In view of the foregoing, it is an object of the present invention to provide a method for manufacturing a semiconductor element that has the proper conditions to be actively formed by droplet discharging. According to the present invention, the high throughput manufacture of a high stable semiconductor element over various sized substrates can be realized in high yields for reduced tact time can be realized.
The followings are aspects of the present invention to solve the foregoing problems.
One aspect of the present invention provides a method for manufacturing a semiconductor element comprises the steps of forming a gate electrode layer by discharging a composite containing a first conductive material over a substrate; forming a gate insulating film over the gate electrode layer; forming a semiconductor film over the gate insulating film; forming a semiconductor film containing an impurity element of a single conductivity type over the semiconductor film; forming a source region and a drain region by discharging a composite containing a second conducive material over the semiconductor film containing an impurity element of a single conductivity type; forming an insulating film over a portion serving as a channel region in the semiconductor film; and forming an island-like semiconductor film by removing the semiconductor film using the source electrode, the drain electrode, and the insulating film as masks.
That is, a gate electrode layer is formed by droplet discharging over a substrate; a gate insulating film, a semiconductor film, a semiconductor film containing an impurity element of a single conductivity type (hereinafter, single conductivity semiconductor film) are stacked by a thin film formation method such as CVD or sputtering; and a source electrode and a drain electrode are formed by droplet discharging. Then, a source region and a drain region are formed by removing the exposed single conductivity semiconductor film by etching or the like. And then, an insulating film capable of being formed by droplet discharging or the like is formed thereover to cover to prevent the portion serving as a channel region of the semiconductor film from removing. In addition, the insulating film serves as a channel protecting film. An island-like semiconductor film is formed by removing the exposed semiconductor film by etching or the like by using the source electrode, the drain electrode, and the insulating film as masks. Through the foregoing process, a semiconductor element that seems like a channel protective type apparently can be obtained. Moreover, a desired liquid crystal display device or a light-emitting device can be obtained by providing a light-emitting element using a liquid crystal element, organic electroluminescent element, or the like, which is formed by connecting a pixel electrode to the source electrode or the drain electrode.
Another aspect of the present invention is that at least a portion provided with a gate electrode layer in a substrate is pretreated before discharging a composite containing a first conductive material over the substrate. As the pretreatment, the formation of a layer containing titanium, titanium oxide, or the like; the formation of a film formed by a substance which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent; plasma treatment; or the like can be nominated. The plasma treatment is preferably conduced in atmospheric pressure.
More another aspect of the present invention is that a source region and a drain region are formed; a first insulating film is formed over the source region and the drain region by CVD or sputtering; a second insulating film is formed over the first insulating film and over the portion serving as a channel region in the semiconductor film; and an insulating film serving as a channel protective film is formed to have a two-layered structure. The second insulating film serves as not only a channel protective film but also as a mask for removing a first protective film formed all over a substrate by CVD or the like. As the first insulating film, an insulating film containing silicon, preferably, a silicon nitride film is used. As the second insulating film, any insulating film can be used as long as it can be selectively formed by droplet discharging. Preferably, a film formed by a substance which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent can used as the second insulating film. The insulating film is not limited to a two-layered structure; the film can be formed to have a three or more laminated-layer.
A substance, which has a skeleton formed by the bond of silicon and oxygen, and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent is referred to as siloxane-based resin. The siloxane-based resin is a kind of a heat resistant planarization film or a heat resistant interlayer (HRIL) film. Hereinafter, the term “heat resistant planarization film”, “heat resistant interlayer film”, “heat resistant resin”, or “HRIL” includes the siloxane-based resin.
As droplet discharging for forming the conductive material or the insulating film, not only ink jetting but also offset printing or screen-printing can be used depending on the property of a film to be formed.
A semiconductor element according to the present invention comprises a layer containing titanium or a titanium oxide formed over a substrate; a gate electrode layer formed over the layer; a gate insulating film formed over the gate electrode layer; a semiconductor film formed over the gate insulating film; a pair of n-type impurity regions formed over the semiconductor film; an insulating film that is interposed between the pair of n-type impurity regions and that is formed over the semiconductor film; and a conductive layer formed over the pair of n-type impurity regions.
The insulating film is preferably formed to have a thickness of 100 nm or more to serve as a channel protecting film. Further, the insulating film may be formed to have a laminated-layer structure. For example, a bottom layer may be formed by a film that can be formed by CVD or sputtering such as a silicon nitride film, and a top layer may be formed by a film that can be formed by droplet discharging, for example, heat resistant resin such as polyimide, acrylic, or siloxane. Alternatively, both layers may be formed by films that can be formed by droplet discharging. The semiconductor film provided with the insulating film is preferably formed to have a thickness of 10 nm or more.
Conventionally, a source region and a drain region were formed by etching off a single conductivity semiconductor film after forming an island-like semiconductor film. Accordingly, it was necessary to provide a resist mask before forming an island-like semiconductor film. On the contrary, according to the present invention, after that a source region and a drain region are formed, an insulating film serving as a channel protective film is formed to cover a portion for serving as a channel region, then, an island-like semiconductor film is formed. Accordingly, a resist mask is not required to be formed, and so a process can be simplified. As discussed above, the present invention provides a novel means for forming a semiconductor element by combining a method for removing a single conductivity semiconductor film using a metal mask of a source electrode and a drain electrode to form a source region and a drain region, and a method, which is specific to a channel protective type, for forming a channel protective film to prevent a channel region from removing. According to the foregoing embodiment of present invention, a semiconductor element can be manufactured by using only a metal mask of a source electrode and a drain electrode without using any resist mask.
Before discharging a composite containing a first conductive material over a substrate, a pretreatment such as the formation of a titanium oxide (TiOx) or the like may be conducted over the substrate at least over the portion provided with a gate electrode layer. Accordingly, the adhesiveness between the substrate and a conductive film such as the gate electrode layer formed by droplet discharging can be improved.
By forming a semiconductor film provided with the insulating film to have a thinner thickness than that of the other semiconductor film, an n-type impurity region can be divided into a source region and a drain region completely. By forming the semiconductor film provided with the insulating film to have a thickness of 10 nm or more, enough large channel mobility can be obtained.
By forming the insulating film to have a thickness of 100 nm or more, the function as a channel protective film can be improved and the channel region can be surely prevented from damaging. Accordingly, a stable semiconductor element having high mobility can be provided. Further, to obtain the foregoing advantage, it is effective that the insulating film is formed to have a two-layer structure composed of a first insulating film and a second insulating film, or three or more laminated-layer structure.